1. Field of Invention
The present invention relates to a semiconductor fabrication process and equipment. More particularly, the present invention relates to a front opening unified pod and associated method for preventing outgassing pollution.
2. Description of Related Art
Following the rapid increase in the level of integration for semiconductor devices, accuracy in dimension as well as material composition in each fabricating step has become increasingly important. Any minor error or pollution may lead to serious production loss or scrapping of a large quantity of wafers.
In semiconductor production, the processing station used for fabricating semiconductor devices typically includes a plurality of modules (for example, processing transport storage/safety link/gaseous reactant). In addition, the processing station may include a wafer transfer system for transporting wafers between various processing modules and the storage modules. In general, wafers are retrieved from a wafer carrier using a specially designed robotic blade and transferred to a processing chamber for a reaction. After the reaction, the wafer is transferred from the reaction chamber back to the wafer carrier so that a subsequent processing step can be initiated.
A conventional 8-inch wafer uses a type of wafer carrier called a standard mechanical interface (SMIF). However, as manufacturing technology continues to improve, the size of wafer that can be processed has increased to 12 inches. To accommodate larger wafers such as the 12-inch wafers, a specially designed wafer carrier called the front opening unified pod (FOUP) has been developed. The FOUP has an air-sealed chamber for holding wafers so that dust particles suspended in the air are prevented from polluting the wafers. When wafers need to be loaded into a piece of processing equipment, the door of the FOUP is opened so that a robotic blade is permitted to pick up a wafer inside the sealed chamber.
FIG. 1 is a top view of a conventional wafer-processing semiconductor fabrication station. As shown in FIG. 1, the processing station 100 includes a reaction chamber 102, a load-locking area 104, a mini-environment area 106, a couple of robotic blades 108, 110 and a front opening unified pod base 112.
Before carrying out a reaction process, the front opening unified pod 114 needs to be secured tightly to the front opening unified pod base 112. To transfer wafers into the reaction chamber 102, the robotic blade 108 inside the mini-environment area 106 is used to pick up a wafer inside the front opening unified pod 114 and then the wafer is downloaded onto a wafer boat 116 inside the load-locking area 104. Thereafter, the robotic blade 110 is used to transport the wafer boat 116 into the reaction chamber 102. After the processing reaction, the robotic blade 110 is again used to move the wafer boat 116 out and then the robotic blade 106 is again used to transfer the wafer inside the wafer boat 116 into the front opening unified pod 114. The aforementioned steps are repeated until all the wafers inside the front opening unified pod 114 have been processed.
In the aforementioned process, a single wafer is reacted each time. However, most front opening unified pods are capable of holding a few tens of wafers. Hence, it takes some time to process the whole batch of wafers inside the front opening unified pod. If the processed wafers inside the front opening unified pod generate some outgassing, the gas (for example, phosphene) that diffuses out of the wafer may fill up the entire space within front opening unified pod leading to some contamination of the untreated wafers. Through such contamination, yield of the processing reaction will drop.